FTL neutrinos (or not)

October 3, 2011
By Steve Nerlich, Universe Today

Location of the Grand Sasso OPERA neutrino experiment in Italy - which receives a beam of neutrinos from CERN - and at faster than the speed of light, if you can believe it. Credit: CERN

The recent news from the Oscillation Project with Emulsion-tRacking Apparatus (OPERA) neutrino experiment, that neutrinos have been clocked travelling faster than light, made the headlines over the last week  and rightly so. There are some very robust infrastructure and measurement devices involved that give the data a certain gravitas.

The researchers had appropriate cause to put their findings up for public scrutiny and peer review  and to their credit have produced a detailed paper on the subject, beyond just the media releases we have seen. Nonetheless, it has been reported that some senior members of the OPERA research team declined to be associated with this paper, considering that it was all a bit preliminary.

After all, the reported results indicate that the neutrinos crossed a distance of 730 kilometres in 60 nanoseconds less time than light would have taken. But given that light would have taken 2.4 million nanoseconds to cross the same distance  there is a lot hanging on such a proportionally tiny difference.

It would have been a different story if the neutrinos had been clocked at 1.5x or 2x light speed, but this is more like 1.0025x light speed. And it would have been no surprise to anyone to have found the neutrinos travelling at 99.99% of light speed, given their association with the Large Hadron Collider. So, confirming that they really are exceeding light speed, but only by a tiny amount, requires supreme confidence in the measuring systems used. And there are reasons to doubt that there are grounds for such confidence.

The distance component of the speed calculation had an error of less than 20 cm out of the 730 kilometres path, or 0.00003% if you like, over the data collection period. Thats not much error, but then the degree to which the neutrinos are claimed to have moved faster than light isnt that much either.

But the travel time component of the speed calculation is the real question mark here. The release time of neutrinos from the source could only be inferred as arising from a 10.5 microsecond burst of protons from the CERN Super Proton Synchrotron (SPS)  fired at a graphite target, which then releases neutrinos towards OPERA.

The researchers substantially restrained the potential error (i.e. 10.5 microseconds) by comparing the time distributions of SPS proton release and neutrino detection at OPERA over repeated trials, to give a probability density function of the time of emission of the neutrinos. But this is really just a long-winded way of saying they could only estimate the likely travel time, more or less. And the dependence on GPS satellite links to time stamp the release and detection steps represents a further source of potential measurement error.

Some of the complex infrastructure required to infer the travel time of neutrinos across the OPERA experiment. Credit Adam et al.

Its also important to note that this was not a race. The 730 kilometre straight-line pathway to OPERA is through the Earths crust  which is virtually transparent to neutrinos, but opaque to light. The travel time of light is hence inferred from measuring the path distance. So it was never the case that the neutrinos were seen to beat a light beam across the path distance.

The real problem with the OPERA experiment is that the calculated bettering of light speed is a very tiny margin that has been measured over a relatively short path distance. If the experiment could be repeated by firing at a neutrino detector on the Moon say, that longer path distance would deliver more robust and more convincing data  since, if the OPERA effect is real, the neutrinos should very obviously reach the Moon quicker than a light beam could.

Until then, it all seems a bit premature to start throwing out the physics textbooks.

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15 comments

Since SN1987A photons were delayed only 3 hours, such eventual effect could drop with time. If just a single one of high order electric or magnetic moment of neutrinos would be nonzero, it would mean that there should be created some Cherenkov radiation. So electromagnetic field should finally slow them down to the speed of light.From the other side, sustaining velocity from OPERA experiment would mean that neutrinos from SN1987A come about 4 years earlier - in 1983 we were not able to observe them ...

As stated in the article this was not a race between a neutrino beam and a beam of light, gravity would not have slowed the light because there was no light to slow. The experiment measured a beam of neutrinos travelling faster than the speed of light in a vacuum which is a well measured and documented speed. They neither performed nor needed to perform any experiments to determine the speed of light in a vacuum as scientists have been doing that for about a century now and have all come up with the same result. Since gravity is not constant at all places on earth if it did effect the speed of light then the speed of light would vary from place on the planet, which it doesn't.

Mekraab, you miss the whole point. The claim IS measured against the velocity of light AS measured in the gravity field here on earth. Gravity has an affect on light nearly everyone agrees with that. Since that is well accepted gravity may have an affect on the velocity of light also, it might slow it down slightly.

I was trying to think of any conceptual errors that could be taking place here, and I really don't see any.

Either it's an error in instrumentation, or the neutrinos really did move faster than light.

Reference frames and gravitational time dilaton from passing in a chord at a different layer in the earth's gravity well do not seem to offer an explanation consistent with the notion that "c" is the limit in Relativity.

Either the experiment is somehow in a measurement error, or it proves Special Relativity and General Relativity are not entirely correct.

Relativity does not even offer a mathematical construct to describe super-luminal velocities, because you end up with a pure, non-complex imaginary number for velocities exceeding "c". I.e. multiples of sqrt(-1)...

Perhaps it could be patched by assigning "c" as the limit of neutrino velocity, rather than limit of "light" velocity...

I think you are missing the point actually. C is a mathematically derived value based on Einstein's Theory of Relativity. This is a fixed number which has been calculated using equations. Over many years and many different experiemnts this value has been experimentally confirmed within a variety of different environments. In fact, light never slows down, it simply appears to slow in the presence of a gravitational field due to the curvature of spacetime. Put simply, space is curved and light has to travel a greater distance, but at the same speed.

So what these scientists are saying is that the Neutrino's appear to have travelled faster than the mathematically derived (and universally accepted to date) value of C.

Ooooh - My - Gawd this data surely makes the true believers scream and the patho-skeptics dance. Old Albert if he is floating around here must be having a ball watching the whole theater of the absurd. To quote Willem Dafoe in an old war movie: "He's just sittin up there drunk as a f&&&^*Ing Monkey and laffin his arse off!" The old boy never intended to be an object of worship, and in truth the main worshipers are mainly bureaucratic Dilberts protecting their jobs and retirements, tenures, ad nauseum. Some real physicists may want to see if space is being stretched along the neutrino's trajectory...and if so...........why?

The slightly superluminal speed of neutrinos has a good meaning in dense aether theory as a counterpart of slightly subluminal speed of photons. You may think about space-time like about surface gradient analogous to water surface. After then two types of solitons - i.e. quasiparticles would always spread along such gradient: the solitons resulting from coupling (mutual wave interference) of surface ripples (which are analogy of light waves) with longitudinal waves of heavier phase (i.e. those which are spreading with subluminal speed like the photons) and solitons resulting from coupling of surface ripples with longitudinal waves of less dense phase - i.e. the neutrinos, which would spread in opposite way, i.e. with slightly superluminal speed. IMO neutrinos are actually a light photinos, i.e. superpartners of photons predicted with SUSY from this perspective.

As I explained already, the experiment should be arranged in the way, the photons pulses resulting from impact of protons into target should be compared directly with neutrinos, which are leaving the target at the same moment with using of telescope or some similar way. Maybe we should consider the hydrogen bomb experiment in free cosmic space in this connection.

Maybe the point could be that the neutrinos, not being subjected to the gravitational force, "skip" the space-time curvature passing trough it. In fact, as we said, the light is bent by the gravitational force, and so when traveling, for example, from Geneva to Gran Sasso in what seems to us a straight line, it run in reality along a little (forth-dimensional) arch from point to point, meanwhile the neutrinos may pass trough the space-time curvature making a straight (or, at least, more straight) 4th dimensional 'route' and then covering less distance. Kind of the iperspace in the science-fiction movies. No?

Yes, it's actually the hyperspace of extradimensions, assumed with string theorists. But these formally thinking people are silly at logical level (they cannot get through shortcuts in causual space-time like the neutrinos) and they don't understand their own concepts.

The point here is, the exactly 3D space is perfectly flat and empty. If it contains something - I mean anything observable - it cannot be 3D anymore. This is simply crucial point and no way is over it.

So, if we have space full of tiny density fluctuations (which manifest itself like the CMBR noise), than it's legitimate to consider it as an extradimensions of the 3D space and to ask, whether all particles (including the particles of light) are traveling through it in the same way. The question is not, if neutrinos could do it - but WHY they should move differently from normal waves of light. This is where the hypothesis ends and actual theory begins.

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